Supraoesophageal lobes in 11 specimens of Octopus vulgaris were split sagitally into two symmetrical halves and isolated by a thin inert mica barrier. Each half-brain is known to control the four arms on its side of the animal and to be able to learn opposite touch paradigms mediated by its four arms. Powdered cytochalasin D was applied directly in each animal to the subfrontal lobe of one half-brain, and both half-brains were then trained to opposite touch paradigms. The cytochalasin treated half-brains could not learn either touch paradigm whereas the control half-brains learned readily. In another set of four animals, cytochalasin D was similarly applied but to the vertical lobe of one half-brain. In this case all the half-brains learned the touch paradigm.